Fundamentals of a relationship
by ecwecwecw1
Summary: Billy and Mandy are in High School now. While some parts of there relationship has changed, the Fundamentals are still the same. BillyxMandy, one shot.


**Authors Note: **In between working on the Double Date for my LincolnxTabby series, I was also watching The Grim Adventures of Billy and Mandy. And one conclusion I came up with was there is no way that Mandy doesn't have some kind of romantic feelings towards Billy. Seriously, look at highlight videos of their relationship on YouTube. She puts up with a lot more from him then she does from anyone else. There has to be a reason for that.

So I decided to write this fanfiction about what it would be like if Billy and Mandy dated in High School. I tried to keep the Fundamentals of there relationship the same, because I think that's exactly how it would be if they dated.

I hope you enjoy.

* * *

Billy ran around the High School, his bag in one hand and a piece of paper in the other. He was looking for Mandy, wanting to share his good news with her. As he ran, he saw two familiar faces in the distance.

"Hey Irwin, hey Puddin," He yelled, running up to them.

They looked at their friend and gave a smile. "Hey Billy, what's up yo?" Billy stopped and looked at the roof. Irwin gave a quite grumble and said, "I mean, what's on your mind?"

Billy smiled. "Nothing, I just wanted to ask if either of you have seen Mandy?"

Irwin gave a sigh, as he leaned against his locker. "Of course I've seen her." Billy saw his eyes turn to love hearts. "She is in my locker. In the air that I breath. In the expired food that is in the cafeteria."

Billy ran over to Irwin and put his hands on his shoulders. "Irwin, you have to open your locker now!" he gave his best friend a shake.

"Why, yo?" he asked as Billy shook him.

"If you leave Mandy in there any longer with your expired food, she's going to kill you."

Puddin chuckled, grabbing Billy's hands and making him let go of Irwin. "Irwin was kidding Billy. We don't know where Mandy is."

Billy looked at Irwin and gave him a glare. "That wasn't a funny joke Irwin."

Irwin took a minute to recover from Billy's violent shaking. "Why do you want to see her anyway?"

Billy grinned and showed his two friends the piece of paper. They quizzingly looked at Billy. "I don't get it?" Irwin said.

"Can't you see the grade right here?" he said, pointing at the paper.

Irwin sighed as Puddin grinned. "Billy, you need to turn it around so we can see the grade, because all we see is a blank piece of paper."

Billy looked at the piece of paper and then at his two friends. He did this a couple of times before it clicked with him. "Oh yeah." He flipped it and pointed at the grade. "See, a C+ in English."

Irwin patted Billy on the shoulder. "Good job yo. You passed first time for once."

"Thanks Irwin." Billy said. "I can't wait till Mandy sees."

Someone tapped Billy's shoulder. "Excuse me... Billy?"

Billy turned around and recognised the person. "Hi-ya Penelope." He gave her a smile.

She blushed slightly. "Hey Billy, what's up?"

Billy looked up. "Well, I can't really see beyond the ceiling and the lights. But I hope there are no clouds up and it's a sunny day when we get out of school."

Penelope giggled. "Oh Billy, you're so funny."

"Gee, thanks." Irwin and Puddin smiled at Billy's obliviousness at what was happening.

"So Billy. I want to ask you what you're doing after school."

* * *

Mandy stomped throughout the school a sour look on her face. Fellow students tried to avoid eye contact with her, and the ones that made the mistake of looking, got a glare in their direction. It wasn't long until she was out of this teenage prison for freaks and idiots.

Speaking of idiots, where was Billy? Normally he can find her no matter where she was. And if he couldn't find her, she'd be able to point him about because of his stupid, loud laugh.

"Heh-heh-heh heh!"

As if on cue, she heard him. She walked in the direction. As Billy came into view, her eyes started to burn with fury when she saw who he was talking to. She hated that Penelope girl. Mandy hated how she made goo-goo eyes at Billy, she hated how she would laugh at anything he said, but most of all, she hated how Billy didn't see through her.

She was about to stomp over there and give her a piece of her mind, when a familiar ginger girl stepped in front of her.

"Well, well, well... Well-well, well, well, well... Well, if it isn't the princess of ugly."

"Please, not now," Mandy grumbled under her breath. "What do you want now Mindy?" She asked, glaring at the ginger and her two cronies that stood either side of her.

"I just wanted to know why they let zoo animals in here?" As she said that, her two friends giggled. "Last time I checked, our High School was a respectable establishment. We don't need any wild boars."

"If they didn't allow animals here then our football team; the rabid ferrets, wouldn't need you - the team mascot." Mandy slightly smirked at the scowl on Mindy's face and the shock reaction of her two friends. "Now out of my way."

"Not so fast Mandy," she said, blocking her. "I'm not finished with you."

"Mindy," Mandy said through clenched teeth, her hand forming a fist. "You better get out of my way."

* * *

As Penelope continued to talk, Billy glanced over and smiled when he saw Mandy. She looked angry.

"Excuse me Penelope." He said with a wave.

"What's the matter Billy?"

Ignoring her, Billy ran over and wrapped his arm over Mandy's shoulder.

"Hey Mandy!" he cried.

Mandy looked up and saw Billy. "Get your arm off of me Billy," she growled.

Billy did as he was told with a smile. He showed her his grade. "Check it out Mandy!"

She looked at the piece of paper. "Well you manged to pass first time, even if it was just barely."

"Uh-huh, and it's all thanks to you." He engulfed her in a bone crushing hug, lifting her up in the air slightly.

Mandy took a deep breath. "Billy, put me down." Billy did as he was told. Mandy stretched her arms. "Thanks," she said, before smacking him upside the head.

"Aw, look at the two dirty love birds." Mindy said mockingly. "It's enough to make me sick."

Billy looked at the ginger girl. "Hi Blandy." he said cheerfully.

"It's Mindy." She snapped.

Mandy smirked at Mindy's reaction. "Come on Billy, let's get out of here." She grabbed him by the arm and dragged him off.

"See you Whingy." He called out, giving Mindy a wave.

"That's not my name you idiot!" She yelled.

"Yeah, but it suits you better," Mandy said under her breath.

* * *

"Eventually the school day would end and Mandy would go to Billy's house to tutor him for his next test. And what is his next test you ask?" Sir Raven took a drink from his goblet. "Why it's a math test. So, let's watch the two teens learn about numbers."

"LEARN ABOUT NUMBERS!"

* * *

Billy looked at the question in front of him, his eyes focusing on the words so much it felt like they were going to roll out of his head. Suddenly a burst of inspiration came to him and he quickly scribbled down something.

"Is that right Mandy?" he asked, showing her what he just wrote down.

Mandy glanced down at the paper and grimaced. "You drew a picture of a pie."

"Yep!" Billy said proudly. "That's a number, right?"

Mandy took a breath before grabbing Billy's hat and whacking him of both cheeks with it. "I am not explaining how to do the formula again. Start using whatever you have in your head or I'm leaving."

Billy saluted. He looked back at his paper, an extra bit of determination in his eyes. Mandy almost smiled when she saw how hard Billy was trying.

"Billy." He looked up at Mandy. "I appreciate what you did early today."

Billy titled his head. "What did I do Mandy?"

"Don't play dum-" she stopped herself, realising what she was saying. "I mean when you came over and stopped me from doing something to Mindy. You saw me and realised I was going to hit her, didn't you?"

Billy gave her a big smile and nodded. Billy may be an idiot, but he knew that if Mandy got into anymore fights, she was going to be in big trouble. So, if he saw her about to hit someone, he'd try to get Mandy away as fast as possible.

Mandy gave him a pat on the head. "You did good." She noticed he was looking at her with a frown. "What?"

Billy hesitated before saying, "Is that it?"

"What do you mean?" she said, leaning her chin on the back of one of her hands. She smirked as she saw Billy chewing his bottom lip, trying to think of the right way to say what he wanted to say. "Could it be you want a reward?"

Billy looked up at her and his face light up as he nodded furiously. Mandy gently took hold of his chin and leaned forward. When she was centimetres away from his lips, she pulled back and looked at her papers.

"No, I don't think you deserve one."

Billy's jaw dropped. "Why not?!" He bellowed.

"Because I saw you talking to that girl again," she said, not look at him.

"What girl?" he asked, scratching his chin. "Do you mean Penelo-"

"Yes! That one," she growled, not wanting to hear Billy say her name.

"But Mandy!" he whined. "She's just a friend. And you know I'd never betray you!"

She glanced at him, "And not just because I'd kill you if you did." It wasn't a question.

Billy nodded, which almost made Mandy smile. She leaned in and gave Billy and feather light kiss on the lips for a second, before pulling back and looking at his blushing face.

"You happy now?" she asked. Billy answered with a grin. "Good, now let's get back to work."

Billy giggled. "If the others at school could see you as you are right now, they would-"

The sound of Mandy's pen snapping in half stopped Billy from talking.

"Billy." Her voice was very low.

"Y-yes?" he asked, his hands moving to his sides.

"What are the three rules?" When Billy didn't answer right away, she glared right into his eyes. "Well?!"

"Number one, don't walk around naked. Number two, don't ever, ever cheat on you."

"And number three!"

"Don't tell anyone that we're dating, or you will make me suffer."

Mandy took a deep breath. "Never forget those three rules Billy. Now get to work, I don't have all day."

Billy nodded and the two continued to work in silence.

* * *

"And so, Billy did not tell his and Mandy's secret, like he had been doing for months. However, in two weeks their secret would be eventually discovered." Sir Raven flipped to the next page in the book. "And since the two weeks in between are boring, let's skip right to that shall we?"

"SHALL WE?!" he repeated with a bellow, flipping through more pages. "Once again, the two children would be studying, but this time, at Mandy's house. The subject was chemistry, one of Billy's weakest subjects."

* * *

"Alright Billy, what's Pb?"

"Lead!" Billy responded.

"Ti?"

"Titanium!"

"Au?"

Billy opened his mouth to respond but stopped. He wasn't sure about this. He racked his brain, trying to figure out what it was.

"You got three seconds Billy." Mandy said.

"Gold?" Billy blurted out.

Mandy smiled. "Very good Billy. You got 30 right in a row." She gave his back a rub.

"Thanks, but it's only because I got you teaching me Mandy." He said, a stupid grin on his face.

"Good answer," Mandy said, leaning over to Billy. "I think you've earned a reward." She then leaned in and gave him a kiss on the lips. This was different then their regular kisses, Mandy was really pressing her lips down. Enjoying the more aggressive kiss, Billy put his hands on Mandy's sides to better enjoy it.

"Which one of you two has moved my blasted scit-Oh my goodness?!"

Mandy and Billy froze as their best friend and slave the Grim reappear walked into the room and saw them kissing. Mandy looked particularly stunned that they got caught.

"Um, what's going on here mon?"

Mandy's face became dark. "Billy, go play outside."

"U-um Mandy?" Billy said timidly. "Am I in trouble?"

The pen snapped in half in Mandy's hands. "Now Billy!" Billy didn't need any more instruction. He ran out and played in Mandy's garden. Mandy then turned her attention to her slave. "Grim. Sit. Now."

Grim sat down, a smile on his bony teeth. "So, you two are finally together. Tell me, how did you two lovebi-"

"Grim," Mandy said, her voice filled with darkness. "If you tell anyone, I will make the remaining time you have as our servant the most painful experience of your life."

Grim saw a darkness emanating from Mandy. "I think it is already the worst experience I've ever had mon."

"I can make it worse," Mandy growled. "Tell no one. Understand?!"

Grim nodded his skull so furiously, it almost came off his head.

"Good," Mandy said. She noticed that Grim made no move. "Do you need something?"

"Well… I was wondering, how did you two end up going ou-" Grim stopped when Mandy glared at him again. "I-I just mean, there's no harm telling me, right? I am your best friend slave."

Mandy continued to glare at him, before casting her gaze towards the table. "It just happened."

Grim leaned in, "What was that?"

"I said it just happened!" Mandy snapped. "I don't know how to explain it. Billy has always been my best friend. I've tolerated more from him then I would from anyone else. Then I started to notice feelings. Instead of trying to fight them, I told Billy we were going out. He said he was fine with that and that's how it happened."

"Aww, aint dat sweet." Grim said chuckling. Mandy grabbed Grim by his cloak and forced him to look her in the eye.

"Not one word."

"N-no problem." He quickly responded.

Mandy let him go. She then went over to the window. "Billy, come in now!"

Billy came running from the garden into the Kitchen. He stood in front of Mandy, a nervous look on his face.

"Grim knows now." Mandy said, sitting back at the table. Billy stood there, waiting for Mandy to say more. "He won't tell, now let's get to work."

Billy nodded and went to sit next to Mandy.

"By the way Grim, I loaned Sperg your scythe. He said he'd bring it back before 6."

Grim glared at Mandy, but she didn't even look up at him. "Damn kids, giving away what's mine." He grumbled, walking away.

"Um Grim?" Billy said timidly. Grim stopped, looking at his moronic master. "What do you think? You know, of me and Mandy."

Mandy glanced at Billy. She was about to tell him off, but noticed he seemed very nervous. Mandy looked at Grim. "Answer him."

Grim smiled. "Billy, I am the Grim Reaper. Ultimate lord of the underworld. Evil is the only thing coursing inside me. And the two of you dating, is a match made in hell in my eyes."

Billy thought about it for a few seconds before smiling. "Thanks, Grim."

Grim said nothing as he left the room.

Billy looked at Mandy and noticed her face was bright red. "Mandy, are you ok?"

Mandy snapped herself out of it, flipping through the pages. "Let's get back to work."

Mandy froze when she felt Billy put his hand on top of hers. When she looked at him, she could tell there was something on his mind.

"What is it Billy?" she asked bluntly.

"Am I in trouble?"

Mandy shifted closer to him, intently focused on him. "That depends, have you done something that would get you in trouble?"

Billy swallowed. "Grim found out. Are you mad?"

Mandy's gazed softened. She took a breath and shifted their hands so hers was on top of his. "Billy, I was the one who kissed you. I felt comfortable in my own house and I let my guard down. I took the risk and that's how we got found out. It wasn't your fault, understand?"

Billy visibly relaxed. He then gave Mandy a goofy grin. "So if it wasn't my fault, does that means it's your-" Billy stopped when Mandy vice gripped Billy's hand.

"Don't push it," she growled. Billy didn't say anything, but the look in his eyes was enough of a confirmation. Mandy let go of his hand, smirking at the fear in his eyes. "Now, let's get studying."

* * *

Sir Raven took a long swig of his goblet before speaking. "But alas, you know what they say about secrets." When no one responded, Sir Raven grew angry and cried, "WELL IF YOU DON'T KNOW, HOW SHOULD I?! The point is, their secret would be revealed. Let's watch it unfold."

* * *

"Mandy!" Billy called, running towards his girlfriend, his arms open for a hug.

Before he could engulf her however, Mandy grabbed him by his shirt. "Don't even think about it." She released Billy and began walking down the school halls, Billy following not to far behind.

"I got an 8 in Chemistry!" Billy showed her his paper. Mandy took it from his hands and had a looked. His actual grade was a B.

Mandy stopped and handed him back his paper. "Good job. I'll met you in the cafeteria. I need to go to my locker."

"Roger." Billy said with a salute, before walking ahead of her.

Mandy couldn't help but be proud of the improvement in Billy's grades. If he kept this up, there might be a day where he might not need her help. But if he ever said such a thing out loud, he'd be taught a lesson.

Mandy's mood grew sour as she saw leaning against Mindy leaning against her locker. She couldn't see those two mindless drones with her, which either means she wasn't looking for a fight, or she really was.

"Well, well, well, we-"

"Mindy, you have 5 seconds to get off my locker." She growled.

"Or what?" Mindy said with a smile. "You know Mandy, your face has been regular ugly instead of angrily ugly for a while now and I am curious as to why."

"Mindy," Mandy growled out.

"It's one of two things. Either you are so scared of getting kicked out you have to hold back." Mindy leaned her face right up to Mandy's. "Or, you have a boyfriend."

Mandy felt her temper flaring up.

"So, which is it Mandy?" Mindy poked Mandy's chest. "Which? Huh? Huh? Huh? Huh?"

Suddenly, Mindy was yanked out of the blonde's face. Mandy looked up and saw Billy, who had yanked Mindy back to get out of her face.

"Mindy! That's enough! Leave Mandy alone!" He sounded really angry as he stepped in between the two girls.

Mindy looked surprised for a second, but that was quickly replaced by anger. "Don't touch me, booger breath." In a split second, Mindy gave Billy a slap across the face.

When Mandy saw Mindy hit Billy, she felt her bubbling anger burst into fury. She pushed Billy aside and grabbed Mindy by the collar, slugging the ginger in the cheek with her fist. Mindy hit the ground with a thud. She lifted her face up, holding her swollen cheek.

"What's wrong with you, you psycho?!"

"If you ever touch my boyfriend again, you won't get back up!"

Mindy eyes grew, for once not having an immediate come back. It didn't talk long though for her face morphed into a smirk. "I always knew you'd end up with this brain-dead loser!"

Mandy was about reach down and grab Mindy by the throat, but Billy grabbed hold of Mandy and held her back.

"Don't! She isn't worth it!"

"That's enough!"

The three looked down the hall and saw Principle Goodvibes staring at them, looking very unhappy.

Mindy stood up and ran towards the Principle. "Did you see what that brute did to-"

"Mindy, I want you in my office now!" Mindy gulped. No one had heard him raise his voice like this, ever. Mindy did as she was told and went to his office. He then looked at Billy and Mandy. "Mandy, wait outside my office. I will be talking to you after."

Mandy nodded.

Billy put his hand on Mandy's shoulder. "Mandy, I can go with you and explain-"

She looked at Billy and said, "Wait for me in the cafeteria." She didn't wait for him to respond. The last thing she wanted was for Billy to be in trouble as well.

She walked to the office, noticing there was a lot more people in the hall, all of them whispering to one-an-other. It looks like some of them heard what she said about Billy being her boyfriend.

"Damn it."

* * *

Mandy had sat outside Principle Goodvibes door for a while, thinking about how she lost her temper, how she reviled her secret and how she might be getting kicked out of school on top of that.

She was brought out of her thoughts when the door burst open and Mindy trudged out, not looking very happy. Mandy heard her mumble something about "Ugly people sticking together".

It looks like Mindy got punished. Well, at least she got to see Mindy get taken down a peg before being kicked out.

"Mandy, you can come in now."

Mandy stood up and walked into the office. She sat in front of his desk and said, "Are you expecting me to apologise?"

The Principle smiled. "Do you think you need to apologise for getting annoyed at a girl that came to you clearly looking to pick a fight?"

Mandy raised an eyebrow.

"Do you think you need to apologise for standing up for your boyfriend after someone hit him? Do you need to apologise for only hitting her once and warning her that you'll do it again if she pushes you?"

Mandy smirked. "No, I don't."

"I don't either." He said with a smile. "Mindy is the one in trouble and she will get her punishment."

"So, I get to hit Mindy and she gets in trouble?" Mandy couldn't hide her satisfied grin.

Goobvibes frowned at the look on her face. "On this occasion. Don't make a habit out of this. If I hadn't witnessed it myself, I may have had to punish you on second-hand information. And your record wouldn't have made it a good punishment. "

"I'll keep that in mind," she replied, the grin didn't leave however.

"That's all I asked." Goodvibes said with a smile.

"May I leave now?" she asked.

He nodded. "I'm sure your boyfriend is waiting."

Mandy frowned at the teasing comment but decided not to push her luck any further today. She stood up and made her way out of his office.

As soon as she was out the door, she saw Billy waiting for her. He walked up to her.

"Is everything ok?" he nervously asked.

"Everything's fine Billy. Mindy got in trouble, not me."

Billy looked relieved. "Good, Cringey deserves it."

Mandy let out a small laugh when Billy said that. She took hold of his hand. "Let's go get something to eat." She dragged him along with her.

"Um, Mandy are you ok with-"

"Everyone will know at the end of the day," Mandy said, knowing what Billy was going to say. "No point hiding it."

Billy grinned and sped up to walk side by side with his girlfriend. "Well, I guess I'm not in trouble either, since you are the one who told everybody."

Mandy raised an eyebrow when she heard that. She was impressed that her boyfriend had the nerve to say that cocky statement, but she couldn't let him get away with that. She stopped and made Billy look at her.

"You know, I would've been fine against Mindy," she said, leaning towards him. "It was only after you stupidly got involved that I said and did what I did."

Billy gulped.

"Yes, I don't think I would've said that at all if you hadn't gotten involved. It takes a lot for me to lose my wits, and you're a master of it."

"But M-Mandy-"

"So it was your fault Billy, and you will be punished." Her face morphed into an evil grin. "You and I will be watching that recent two-part horror film."

A cold chill ran down Billy's spin as he began to tremble. "Y-you mean the one with th-the-"

"The one with the clown Billy."

"But if I watch that he'll destroy us al-"

Mandy put a finger on his lips to stop him. "If you last both parts, you will be rewarded."

* * *

"Billy would manage to make it through both films and he would get his reward. And yes, it is exactly what you think it is." Sir Raven then slammed his book shut. "But if you expect me to tell you about it in detail, then you need to get a girlfriend."

Sir Raven placed the book on the table and took a breath. "The point of this story is that no matter how things change for Billy and Mandy, the fundamentals of the relationship will always be the same. Now have a good night."

"HAVE A GOOD NIGHT!"

The End

* * *

**Authors Note:** I hope no one found the Sir Raven parts mean. He was one of my favourite recurring characters in the show and I wanted to have him in the fanfiction.

I hope you all enjoyed it. Have a good Christmas.


End file.
